Tour Stop 12: Trees and Storm Water

Trees like the large Water Oak in front of you have many benefits, but here’s one you may not have thought about: trees actually influence the flow of rain water, helping to protect against flooding and to improve water quality in the urban environment.

How do they do this? Think about what happens to water during a heavy rain. If it falls on a surface like a concrete parking lot, all of the water quickly flows into a storm sewer. Not only does this increase the risk of flooding, but it also washes chemicals and litter from roads and parking lots into our bayous.

Now think about what happens to rain falling in a forest. In a process called vertical detention, the leaves, branches, and bark break the fall of the raindrops, slowing down their progress to the ground. A lot of the captured rainwater evaporates back into the air. The water that does reach the ground is more likely to sink in and less likely to run away, because the tree’s roots make the soil more porous. And these same roots move water up from the soil into the leaves, where it eventually comes out through tiny pores on the underside of the leaves and away into the air.

So how does this all add up? A big tree like this can soak up as much as 140 gallons of water a day through its roots. There are over 1,200 trees this size or larger at West 11th Street Park. That adds up to 168,000 gallons of water a day, and that’s not even considering the thousands of smaller trees, not to mention the water that’s absorbed into the ground and the water that evaporates from the leaves and branches. That’s quite a benefit!

If you want to read more about this, the link below will take you to a website that will tell you more about the effect of trees on storm water runoff: National Tree Benefit Calculator.